To push back against this criticism, the proponents of the causal modelling framework might observe that at least for the moment it seems that not all possible process matrices actually occur in reality - at present we only know how to implement the causal ones. Therefore one might be tempted to argue that the reason we see only causal process matrices is that reality is fundamentally `causal' in the sense of strong causation, and thus the only processes which can occur are the ones which have an underlying causal structure. This would seem to justify the methodology of seeking to come up with an underlying causal structure for the quantum mechanics, including the Bell correlations. However, it remains possible that the non-causal processes are in fact physically possible, and simply occur only in special regimes, such as in quantum gravity[1]} or on closed timelike curves[2]} (after all, CTCs do in fact occur in some solutions to the Einstein Field Equations[3]}). Moreover, even if it is true that only causal processes occur in nature, it remains the case that there doesn't appear to be intrinsic asymmetry in these processes, so there is no reason to invoke specifically strong causation to explain the absence of non-causal processes. At best we have reason to hypothesize that nature is fundamentally causal in the sense that all physically possible processes can be assigned a strict partial order which obeys the signal requirement, and since the signal requirement places no restrictions on no-signalling processes, this hypothesis does not justify us in seeking to come up with an underlying causal structure for the Bell correlations.
